Semiconductor devices containing integrated circuits (ICs) or discrete devices are used in a wide variety of electronic apparatus. The IC devices (or chips, or discrete devices) comprise a miniaturized electronic circuit that has been manufactured in the surface of a substrate of semiconductor material. The circuits are composed of many overlapping layers, including layers containing dopants that can be diffused into the substrate (called diffusion layers) or ions that are implanted (implant layers) into the substrate. Other layers are conductors (polysilicon or metal layers) or connections between the conducting layers (via or contact layers). IC devices or discrete devices can be fabricated in a layer-by-layer process that uses a combination of many steps, including imaging, deposition, etching, doping and cleaning. Silicon wafers are typically used as the substrate and photolithography is used to mark different areas of the substrate to be doped or to deposit and define polysilicon, insulators, or metal layers.
Static induction transistors (SIT) are devices that have been used typically for, but not limited to, high voltage and ultra high frequency applications. Some SIT devices are normally “on” semiconductor devices since the gate voltage (Vg) is normally equal to 0. The reverse bias that can be applied to the gate can expand the depletion region and pinch-off and block the current flow (e.g., the device turns off at Vg of −15V).
Two examples of conventional SIT devices are depicted in FIGS. 10(a) and 8(b). The device depicted in FIG. 10(a) is often referred to as a planar gate SIT and can have a relatively low capacitance but a relatively high specific resistance (Rsp). The planar gate structure is used for higher frequency applications due to its lower capacitance. The device depicted in FIG. 10(b) is often referred to as a recessed gate SIT and can have relatively high capacitance but a relatively low Rsp. While the recessed gate structure can have a lower Rsp, it can be limited by large parasitic capacitance from the dielectric on the side wall of the trench.